The present invention relates to a rare earth permanent magnet having anisotropy and a method of producing the magnet.
Nd—Fe—B type permanent magnets have been widely used as a magnet for a motor. Such magnets have been produced by means of a melting method disclosed in M. Sagawa et al., Japanese Journal of Applied Physics 26 (1987) 785 or a quenching method disclosed in R. W. Lee, Applied Physics Letter 46 (1985) 790. Further, it is possible to produce magnet powder having anisotropy by means of a HDDR treatment disclosed in T. Takeshita et al., Proc. 10th Int. Workshop on Rare Earth Magnets and Their Applications, Kyoto, (1989) 511.
The magnetic properties of Nb—Fe—B type permanent magnets have approached a theoretical limit, and therefore it is desired to develop next-generation high-performance magnets. One of the next-generation magnets is an exchange spring magnet, which is also called nano-composite magnet, as disclosed in E. F. Kneller and R. Hawig, IEEE Transaction Magnetics 27 (1991) 3588. Such an exchange spring magnet has a structure where hard magnetic phases and soft magnetic phases are finely dispersed at intervals of several tens nm. The exchange spring magnet performs like as a unit hard magnetic phase as a whole since the magnetization of the soft magnetic phases is not easily reversed for the reason that the magnetizations of the hard and soft magnetic phases are coupled by the exchange interaction therebetween. Accordingly, it has been evaluated that the nano-composite magnet has a possibility for functioning as a very high-performance magnet. For example, it has been reported in R. Skomski and J. M. D. Coey, Physical Review B48 (1993) 15812 such that if Sm2Fe17N3/Fe type alloy can have a property of anisotropy, (BH)max=137 MGOe will be theoretically obtained. A producing method of Nd2Fe14B/Fe3B type exchange spring magnet has been proposed in R. Coehoorn et al., Journal de Physique 49 (1988) C8-669. Further, a producing method of Nd2Fe14B/Fe type exchange spring magnet has been proposed in Japanese Patent Provisional Publication Nos. 7-173501 and 7-176417 and in L. Withanawasam et al., Journal of Applied Physics 76 (1994) 7065.
However, a melt spun method or mechanical alloying (MA) method employed in the above magnet producing methods cannot produce the magnet having the magnetic anisotropy, and therefore the property of the obtained exchange spring magnet is not sufficient as compared to the theoretical property.
Furthermore, various producing methods of an anisotropic exchange spring magnet have been proposed. For example, Japanese Patent Provisional Publication No. 11-8109 has disclosed a producing method of crystallizing Nd—Fe—B amorphous alloy by heating in a high magnetic field. Japanese Patent Provisional Publication No. 11-97222 has disclosed a producing method of hot working a quenched thin strip alloy so that hard and soft magnetic phases are finely and dispersedly precipitated. Japanese Patent Provisional Publication No. 2000-235909 has disclosed a method of directly producing a magnet having the anisotropy by executing a warm-working uniaxial-deformation under a liquid phase existing condition of the raw material.